It is often necessary to surgically treat spinal disorders such as scoliosis. Numerous systems have been used for spinal correction and fixation. These fixation systems are well known and usually include one or more elongated members, typically either rods or plates, placed along the vertebral column. The elongated member is attached to the spine typically with a plurality of various fasteners, which may include, but are not limited to, pedicle screws, plates, transverse process hooks, sublaminar hooks, pedicle hooks, and other similar devices.
The fasteners are typically implanted prior to their attachment to the elongated member, with the elongated member then being bent and/or cut to be received by the plurality of fasteners. By fashioning the elongated member to fit implanted fasteners, the overall fit of the fixation system is more likely to be proper than if the elongated member is attached to the plurality of fasteners, each fastener in turn then being attached to the spine. FIG. 1 illustrates one such prior art fixation system 1 affixed to a spine 19. Fixation system 1 includes a plurality of fasteners or fixation elements 3 connected by an elongated member or rod 2, which has been bent appropriately to fit the shape proscribed collectively by fixation elements 3.
In an open surgery procedure, the wide exposure of the spine and the surrounding anatomy simplifies contouring the elongated element to the fasteners. However, such exposure can result in significant damage to the soft tissue, particularly the muscles. This damage can lead to weakening in the muscular area, and thus to weakening in the retaining system for the spine or other extremities and also entails the risk of scarring, which, in turn, can lead to postoperative problems.
In an effort to avoid the possible complications associated with open surgical procedures, so-called minimally invasive procedures can be used for implantation of a fixation system. During such a procedure, several percutaneous incisions are made, leaving the posterior back muscles largely intact. The fasteners are then placed through the skin, preferably with the help of a computer assisted surgery system (CAS) such as that described, for example, in U.S. Pat. No. 5,383,454. The fasteners are typically inserted through the incisions using an inserter having a shaft of sufficient length so that the end projects through the skin. In such situations, the sensors or transmitters associated with the CAS can be located on either the end of the inserter or directly on the fastener.
Irrespective of whether a CAS is used during a minimally invasive implantation of a fixation system, contouring the elongated element is problematic because unlike an open surgical procedure, the fasteners are not directly visible and it has not been possible to use a trial rod or a bending template.
Thus, there exists a need for a device for simulating the position and orientation of at least a portion of an implanted fixation system, so that, for example, a spinal fixation rod can be pre-bent for insertion in implanted pedicle screws and/or hooks using a minimally invasive surgical procedure.